1. Field of the Invention
The present invention relates in general to an automatic intermittent energization controller for use in an electrostatic precipitator (ESP).
2. Description of Prior Art
For environmental protection purposes, factory facilities that produce exhaust gases are generally installed with electrostatic precipitators (ESP) to collect pollutant particles contained in the exhaust gas. A typical ESP includes collecting plates arranged in parallel to each other and discharge wires disposed between the collecting plates. A DC power is delivered to the discharge wires so that electrons discharged by the discharge wires, known as corona currents, cause ionizations of the pollutant particles passing through the ESP. The ionized dust particles are attracted by an electric fields established by the DC power to thereby be collected by the collecting plates.
For purposes of energy saving and higher dust-removing efficiency, the DC power delivering to the ESP can be varied in accordance with the concentration of pollutant particles passing through the ESP, i.e. the DC power is supplied with a maximum magnitude when there is detected a very large concentration of dust particles, and the DC power can be reduced when there is detected a low flow of dust particles.
A conventional power controller is shown in FIG. 1, in which an AC power source is used as the main power source generating an AC voltage V.sub.1 (t) having a period of T, T=1/60 for typical industrial power applications, and with a waveform as illustrated in FIG. 2A. A thyristor circuit 20 is used in combination with a thyristor firing control circuit 30 to control the passing or cut-off of full sinusoidal cycles in the AC voltage V.sub.1 (t). A charge period is herein and hereinafter defined as one period including a first predetermined number C of full sinusoidal cycles in the AC voltage V.sub.1 (t) allowed to pass through the thyristor circuit 20; and a pause period, which appears right in subsequence to the end of one charge period, is herein and hereinafter defined as one period including a second predetermined number P of full sinusoidal cycles in the AC voltage V.sub.1 (t) being cut off by the thyristor circuit 20. One charge period and its subsequent one pause period appear alternately with a period of T.sub.1 +T.sub.2.
For an example as illustrated in FIG. 2B, if (C,P)=(5,1), then the thyristor circuit 20 allows five consecutive full sinusoidal cycles in V.sub.1 (t) to pass therethrough and cuts off the subsequent one during a period of 6.T. For another example as illustrated in FIG. 2C, if (C,P)=(2,5), then the thyristor circuit 20 allows two consecutive full sinusoidal cycles in V.sub.1 (t) to pass therethrough and cuts off the subsequent five during a period of 7.T.
The full sinusoidal cycles in V.sub.1 (t) accordingly are sent intermittently via an low-to-high voltage transformer 40 to the AC-to-DC conversion circuit 50, which is used to generate a DC output V.sub.DC in proportion to the average power of V.sub.2 (t). By fundamental electric principles, the output DC voltage is also in proportion to R.sub.c, where: ##EQU1## A larger R.sub.c indicates more consumption of electrical energy, and a smaller R.sub.c indicates less consumption of electrical energy.
The selection of the charge-pause parameter set (C,P) for the conventional ESP energization controller is achieved only by manual input. Once the selection is made, the controller is not adaptive to changes in the flow rate of dust particles. The only way to change the DC power level input to the ESP is by means of input another new set of (C,P) manually. Therefore, the ESP operator has to be sitting by the ESP, monitoring the flow of dust particles and thereby choosing an appropriate set of (C,P) for adaptive control of the dust removing process.